Radiation therapy or radiotherapy is the medical use of ionizing radiation, generally as part of cancer treatment to control or kill malignant cells. Radiation therapy may be curative in a number of types of cancer. It may also be used as part of curative therapy, to prevent tumor recurrence after surgery to remove a primary malignant tumor (for example, early stages of breast cancer). Radiation therapy has been used before, during, and after chemotherapy in susceptible cancers.
Radiation therapy is commonly applied to the cancerous tumor because of its ability to control cell growth. Ionizing radiation works by damaging the DNA of exposed tissue leading to cellular death. Normal tissues (such as skin or organs which radiation must pass through in order to treat the tumor), also receive radiation dose causing cellular damage and death which leads to sometimes serious side effects.